In the related art, there is known a vehicle door opening/closing apparatus that includes a telescopic support member between a body and a door of a vehicle and is capable of holding the door at an open position by the support member (for example, see Reference 1 (JP 2014-100956A)).
Such a vehicle door opening/closing apparatus is disclosed to have a configuration in which an actuator that causes the support member to extend or retract is built into the support member. The support member includes a substantially cylindrical outer housing and an inner housing having a smaller diameter than the outer housing, and extends or retracts by the actuator that causes the inner housing to move in an axial direction in the outer housing. Then, joint members are provided at both end portions of the support member in the axial direction (longitudinal direction) and the joint members are fitted into a spherical fitting portion provided in connection portions on the door side and on the body side.
Incidentally, a configuration, in which such a vehicle door opening/closing apparatus described above includes circumferential engagement portions that engage with an inner circumferential surface of the outer housing and an outer circumferential surface of the inner housing in a circumferential direction, respectively, may be considered. In this configuration, the circumferential engagement portion of the outer housing and the circumferential engagement portion of the inner housing have, for example, protrusions and grooves alternately in the circumferential direction. The protrusion of the outer housing has a shape that protrudes to the inner side in a radial direction and the protrusion of the inner housing has a shape that protrudes to the outer side in the radial direction. The protrusion of the outer housing is positioned in the groove of the inner housing in a state of being assembled to the inner housing, and the protrusion of the inner housing is positioned in the groove of the outer housing in a state of being assembled to the outer housing. In addition, the circumferential engagement portions of the outer housing and the circumferential engagement portions of the inner housing are individually formed to have a predetermined length in the axial direction, such that an engagement state is maintained in the circumferential direction even in a case where the inner housing and the outer housing relatively move with respect to each other in the axial direction.
In this configuration, when the inner housing receives a rotational force from the actuator, a circumferential force is generated between the outer housing and the inner housing. At this time, since rotation of the outer housing is regulated by the joint member of an axial end portion, the inner housing and the outer housing are caused to relatively move with respect to each other in the axial direction such that the support member extends and retracts.
However, since the housings and the joint members are fixed by caulking, there is a concern that the housings and the joint members will relatively rotate with respect to each other in the circumferential direction due to the fixing strength of the caulking between the housings and the joint members when the circumferential force is generated between the outer housing and the inner housing.